Ammonia recovery



Nov. 28, 1933- F. w. sPERR, .JR

AMMONIA RECOVERY Filed Feb. 23, 1932 5ta/erick A 7 R NE Y.

Patented Nov. 28, 1933 laisser eri-rer les AMMoNrA RECOVERY Frederick W.Sperr, Jr., Ventnor, N. J., assignor to The Koppers Company of Delaware,a corporation of Delaware Application February 23, 1932. Serial No.594,455

2 claims. (ol. 23-196) My. invention relates to the recovery of ammoniafrom fuelgases such as coke oven gas, mixed gas, and the like. Itrelates especially to the recovery of ammonia by the so-called indirectprocess in the form of ammonia liquor.

t gas manufacturing plants such as coke oven plants where the majorportion of the ammonia content of the gas is recovered. directly in theform of ammonium sulphate by contacting the gas with sulphuric acid, theproduction of ammoniacal gas liquor ordinarily amounts to about 2Ogallons per ton of coal carbonized. This liquor is produced by coolingand condensingrthe crude gas and contains most of the xed ammoniumcompounds produced during carbonization as well as some free ammonia.The major portion of the free ammonia remains in the gas and issubsequently removed as ammonium sulphate.

At some plants, however, all of the ammonia is removed from the gas inthe form of liquor and the quantity of liquor produced is then aboutthree and a half or four times as great as in plants where ammoniumsulphate is produced, amounting to 8G gallons per ton of coalcarbonized, for example. 0f this amount, about 20 gallons is condensingliquor as in the previous case, and the remaining gallons come from theaminonia scrubbers where the ammonia is washed from the gas with WaterThe ammonia contained in this scrubber liquor is principally in the freeform.

In the past it has been common practice at ammonia liquor plants tocombine the condensing liquor and the scrubber liquor before treatingfor recovery of ammonia. vThe combined liquor Was then delivered to anammonia recovery installation consisting usually of a free ammoniastill,a lime mixing Vchamber and a fixed ammonia still. The liquor Was treatedin the free stillv for removal of free ammonia, mixed with milk of limeor other suitable alkaline material to liberate iixed ammonia, and thenfurther Vdistilled with steam in the iixed still toremove the remainingammonia.

In treating ammonia liquorin thismanner Vthe volumel oi the liquor isincreasedabout 510% to 50%, due to condensation of steam supplied fordistillation and to the addition of milk of lime or analogous alkalineliquids. Consequently at ammonia liquor plants still waste productionfrequently amounts to from 100 to 120 gallonsV per ton of coalcarbonized. In many instances the disposal of such large quantities ofstill waste presents a serious problem, as itis generally necessary toprovide settling basins or other suitable means for clarifying the Wastebefore its discharge to streams, and purification from constituentsother than suspended solids, such as tar acids, is also frequentlyrequired. Y' l An object oi my present invention is to provide a processwhereby the amount of still waste produced at ammonia liquor plants ismaterially reduced. -V

Another object of my inventionis to provide. an improved process ofrecovering ammonia from fuel gases and suitable apparatus therefor.

My invention has for further objects such other operative advantagesandresults as obtain in the process and apparatus hereinafter described andclaimed.

By means of my inventionthe difficulties ordinarily encounteredindisposing of the large.r quantities of ammonia still waste produced inammonia liquor plants are avoided in an eiiicient and economical manner,and I have found-that the amount of still waste produced in theseyplants can be so reduced that it does not materially exceed the amountproduced at plants Where arninonia is recovered in the form of sulphate.

To accomplish these desirable results I collect the aqueous condensateorcondensing liquor from the collecting main, primary-cooler or coolers,the exhauster and tar extractor, etc., in a separate system and distillit in the usual vtype of ammoniastill to recover free and xed ammonia.This system removes substantially all of the xed ammonia from the gals.I prefer to use no freshwater in making up milk of lime for ,this stillbut instead I usea portion of the still waste for this purpose,preferably after clarification. A

Ammonia liquor from the scrubbers collected in a second system anddistilled preferably in a single column ammonia still, without liming,to recover free ammonia. Elliuent from this still is cooled andrecirculated through the scrubbers to treat further 'quantity of gas.This liquor is diluted somewhat by condensation oi steam duringdistillation and by condensation of .Water vapor from the gas, andexcess liquor thereby produced is transferred tc the i'lrst system kanddistilled with the condensing liquor.

I now describe with reference to the accompanying drawing a preferredmethod ci practicing my improved process ofrecovering ammonia from fuelgases. In the drawing The single figure is a partially diagrammaticelevational view, with sections brokenaway, of

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apparatus suitable for the practice of my prese ent invention.

Gas is produced in a coke oven or retort, which is usually one of abattery of similar ovens or retorts, and passes from the oven through anascension pipe 2 into a hydraulic main or collecting main 3. In thismain it is contacted with ushing liquor which cools the gas andcondenses therefrom certain constituents such as tar andy xed ammonia.The gas then passes with the flushing liquor and condensate through anontake pipe 4 into a pitch trap `5. In the pitch trap 5 the gas isseparated from the liquids present, and passes fromthe upper portion ofthe trap through a pipe 6 into a primary cooler 8.

In the cooler 8 the gas is further cooled and condensed by contact withcooling liquor, which is preferably recirculated, and the cooled gaspasses from the cooler through a pipe 9, an exhauster 10 and a tarextractor 11 to the ammonia scrubbers. These scrubbers may be of anysuitable type, such as horizontal rotary scrubbers, or verticalscrubbers packed with suitable Contact materiaLor scrubbers of thebubble tray type, for example.

In the present instance vertical scrubbers 12 and 14 packed withsuitable contact material are used. scrubbing liquor, which ispreferably cooled to the lowest temperature feasible, is passed over thescrubbers in series in countercurrent with the flow of gas, from whichit absorbs ammonia. It is to be understood that if desired any othertype of sc-rubber may be used or a different number of scrubbers of thistype may be used. K

Flushing liquor and condensate from the gas pass 4from the bottom of thepitch trap 5 into a hot drain tank 16. In this tank the aqueousammoniacal liquor or gas liquor is separated from tar, and the tar maybe withdrawn through a pipe 18 for any desireddisposal. Gas liquorsubstantially free from tar passes from the hot drain tank through apipe 19 into a ushing liquor circulating tank 20, from `which it iswithdrawn by a pump 22 and recirculated through a pipe 23, which mayterminate in sprays 24 or other suitable distributing devices, into thecollecting main 3, to cool a further quantity of gas.

kExcess flushing liquor, substantially equal in amount to the aqueouscondensate formed from the gas in the collecting main,'overflows fromthe tank 20 through a pipe 26' into an ammonia liquor storage tank 28.

Cooling liquor after passing downward through the primary cooler' incontactA with the gas, which it cools and from which it condenses afurther quantity of tar and ammoniacal liquor, collects in a sump orwell in or near the bottom of the primary cooler. From this well it isWithdrawn by a pump 30 and Arecirculated through a cooler 31, a pipe 32,and sprays 33 or other suitable distributing devices, ontc the contactma` terialv 34 which may consist of wooden hurdles or other suitablecontacting means. It passes downwardly over this contact material inintimate contact with a further quantity of gas which isthereby cooled.

Tar or other heavy material settles to the bottorn of the sump and maybe withdrawn through a pipe 36. Excess liquor produced by condensationfrom the gas overows through a pipe 38. through which it passes intopipe 26 and thence to `the ammonia liquor storage tank 28.

Further condensation of tar and/or ammoniacal liquor usually takes placein the exhauster 10 and the tar extractor 11. Condensate formed at thesepoints passes through pipes and 4l to a pump 42, or other suitable meansof delivery, which transers it through pipe 43 to the hot drain tank 16where tar and ammonia liquor are separated and separately withdrawnthrough pipes 18 and 19.

Cooled scrubbing Vliquor is delivered through a pipe 45 to the lastammonia scrubber 14 of the series of scrubbers, in which it removesammonia remaining in the gas with which it comes in contact. Gassubstantially free from ammonia passes from the scrubber 14 through apipe 46. The liquor is preferably recirculated from the bottom of thescrubber 14 by pump 47 through pipes 48 and 45.

Excess liquor overflows through a pipe 49 to a pump 50 which delivers itto the preceding scrubber 12, in which it removes at least a part of theammonia from a further quantity of gas. In the present. instance, thescrubber 12 is the iirst of the series of two scrubbers, but any otherdesired number of scrubbers may be employed; through. which the gasv andliquor pass counter currently inseries..

The animoniacal scrubber liquor may be recirculated over the scrubber 12through a pipe 51 and the pump 50. Liquor overflows and passes from thescrubber throughv a pipe 52 to an ammoniated scrubbing' liquor storagetank 53. From this tank it is withdrawn by a pump 54, which delivers itto a single column ammonia still 55 where the scrubbingV liquor isdistilled with steam supplied through a pipe 56. Ammonia is therebyremoved, and passes from the topof the still through a vapor outlet 57forl condensation or utilization.

Stripped scrubbing liquor passes from the bottorn of the still 55through a pipe 58 into a sump or trench 59 or other suitable collectingmeans. From this trench liquor is withdrawn by a pump 6U, and deliveredthrough a cooler 61 and pipe 45 to the scrubbing system.

vExcess liquor, produced by condensation in the still 55A or in thescrubbers, overiiows from the trench 59 through a'pipe 63 and isdelivered by a pump 64 through a pipe 65 to the ammonia. liquorv storagetank 28 in the condensing liquor system. Alternatively, this liquor maybe de livered to. some other part of the condensing system, as to thecirculating tank 20, for example.

Liquor is withdrawn from the storage tank 28 by apump 67 and deliveredto an ammonia recovery installation 68 which preferably consists oa freestill 69 mounted upon a liming chamber 70 and connected with a xed still'71 in theusual manner. Liquor is delivered by the pump 67 to the top'ofthefree still 69 and passes downwardly through this still incountercurrent with steam or other hot vapor which removes free ammoniaandl other volatile constituents from the liquor.

The liquor then continues downward into the lime mixing chamber 70 whereit is mixed with milk'of lime or other suitable alkaline solution orsuspension supplied through a pipe 73. This lime liberates the fixedammonia and the liquor, usually containing some excess lime insuspension, flows from the liming chamber through a pipe into the xedstill '71. In this still the liquor is subjected to further distillationwith steam supplied through a pipe 76 which removes the still, throughwhich itcontinues upwardly, removing free ammonia from a furtherquantity of liquor. Vapors pass from the top of the free still 69through a Vapor pipe 79 for condensation or other disposal. Still wastesubstantially free from ammonia passes from the bottom of the fixedstill '71, preferably through a trap 80 to a settling basin 81 or othersuitable means rof clarifying the waste by removal of suspended solids.

A portion of the clarified waste is withdrawn through a pipe 83 to alime mixing tank 84, and the remainder of the still waste is dischargedthrough a pipe 86 for any desired disposal. In the tank 84 clarifiedstill waste is mixed with lime to form lime suspension or milk of limewhich is delivered by a pump 88 through the pipe 73 to the limingchamber 70, where it liberates fixed ammonia contained in a furtherquantity of liquor.

By the simple procedure described hereinabove I have found it possibleto reduce the still Waste production at ammonia liquor plants tosubstantially the amount produced at sulphate plants without appreciablyadding to the cost of ammonia recovery.

A further advantage inherent in my present process is that whendephenolization of the ammonia liquor is necessary, which is nowfrequently the case, the amount of liquor to be dephenolized is greatlyreduced. Dephenolization may be effected in connection with the presentprocess by scrubbing the liquor withdrawn from tank 28 with animmiscible solvent prior toits introduction into the ammonia stills, orby dephenolizing the liquor after passing through the free ammonia still69 but before entering the liming chamber 70.

In the latter instance dephenolization may be effected by contacting theliquor with steam or other suitable hot gas or vapor, as described inthe copending applications of J. A. Shaw, Serial No. 230,570, ledNovember 2, 1927, and of M. Shoeld, Serial No. 386,515, filed August 17,1929, for example.

It will be obvious to those skilled in the art that variousmodifications can be made in the several steps of my process and theseveral parts of my apparatus without departing from the spirit of myinvention and it is my intention condensed ammoniacal liquor from tar,recircu-A lating at least a part of the separated ammoniacal liquor tocool a further quantity of gas, withdrawing excess liquor from thecooling system, separately collecting the ammoniated scrubbing liquorand distilling it to remove free ammonia therefrom, cooling thedistilled liquor and recirculating it to scrub ammonia from a furtherquantity of gas, withdrawing excess liquor from the scrubbing system andcombining it with the excess liquor withdrawn from the condensingsystem, and treating the combined excess liquor to remove free and xedammonia therefrom.

2. The process of recovering ammonia from fuel gas, which comprisescooling the gas and condensing therefrom ammoniacal liquor and tar, thenscrubbing vthe gas with an aqueous liquid which removes a furtherquantity of ammonia and is thereby ammoniated, separating condensedammoniacal liquor from tar, recirculating at least a part of theseparated ammoniacal liquor to cool a further quantity of gas,withdrawing excess liquor from the cooling system, separately collectingthe ammoniated scrubbing liquor and distilling it to remove free ammoniatherefrom, cooling the distilled liquor and recirculating it to scrubammonia from a further quantity of gas, withdrawing excess liquor fromthe scrubbing system and combining-it with the excess liquor Withdrawnfrom the condensing system, distilling the combined excess liquor withlime to remove free and fixed ammonia therefrom, discharging still wastethereby produced, clarifying the still waste, adding lime to claredstill waste to form a suspension, and adding the lime suspension to afurther quantity of ammoniacal liquor to liberate fixed ammoniacontained therein.

FREDERICK W. SPERR, JR.

